A coupling element for a helix-shaped eccentric screw pump rotor is known from document DE 199 43 107 A1. This document discloses a rotor, the helical shape whereof changes towards the one end, such that this end can be received by a coupling element. For this purpose, the coupling element has an internal profile complementary to the helix-shaped profile of the shaft end. A coupling between the rotor end and the coupling element thus takes place by means of an uninterrupted surface which is complementary to the rotor end. The rotor end is thus screwed into the coupling element in such a way that it is screwed along the helix-shaped inner wall surface up to the stop and is thereby guided along the helix-shaped inner wall surface of the coupling element. Rotating back or unscrewing of the rotor is prevented by means of a cross pin shown in FIG. 1, which forms a rotor stop at the opposite end of the rotor.